The present invention relates generally to ink reservoirs for high speed computer driven inkjet printers and plotters and other applications where precise pattern dispensation of a fluid is required such as the layout of circuit masks. In such printers the ink reservoir is ordinarily maintained under a sub-atmospheric or negative pressure so that ink will not leak or drool from the printhead. Various types of ink reservoirs may be used including refillable ink reservoir cartridges which are mounted on the moveable printer carriage, throwaway replaceable cartridges which are mounted on the printer carriage and remote or offboard ink reservoirs from which ink is pumped to the print head by tubing. In the onboard refillable or throwaway cartridges, a polymer foam is ordinarily provided in the ink reservoir so that the capillary action of the foam will prevent ink from drooling from the printhead. Polymeric foams of the type typically used for this purpose are non-biodegradable and thus cause environmental problems whenever a previously used cartridge is emptied and thrown away. In addition, the use of industrial foam in the ink reservoir restricts the operating pressure range of the ink cartridge and such foam ordinarily leave a chemical residue which is incompatible with and/or reacts adversely with printer ink. Similarly, the relatively long tubing used to convey ink from an offboard pressure reservoir to a printing head does not lend itself well for different printing pressure ranges.
A collapsible ink reservoir for an inkjet printer is disclosed in U.S. Pat. No. 4,422,084 issued Dec. 20, 1983 to Saito. Negative pressure is maintained in a polypropylene ink bag by a spring which biases the bag walls apart from each other.
One example of an onboard ink pressure reservoir cartridge is disclosed in U.S. Patent Application Ser. No. 07/717,735 filed Jun. 19, 1991 entitled SPRING-BAG PRINTER INK CARTRIDGE WITH VOLUME INDICATOR filed by David S. Hunt and W. Bruce Reid and assigned to the assignee of the present invention. The cartridge disclosed in that application basically comprises a rectangular housing containing a flexible bag of ink and an ink filter and a printhead which receives ink from the filter. A spring inside of the bag of ink urges its flexible walls apart from each other thus maintaining a negative or sub-atmospheric pressure in the reservoir which is overcome as ink is emitted from the printhead. Cartridges of this type, while well suited for their intended purpose, suffer from the disadvantage that ink is not always completely used since the spring occupies a certain volume of space inside of the ink bag. As seen in that application, the spring essentially consists of a pair of spaced parallel plates which are urged apart by a spring.
Also of interest is the disclosure owned by the assignee of the present invention titled INK PRESSURE REGULATOR FOR A THERMAL INK JET PRINTER filed on Aug. 12, 1992 by George Kaplinsky and Tofigh Khodapanah, the disclosure of which is hereby incorporated by reference and which discloses various spring configurations for use in pressure regulators.
Experience has shown that despite use of the spring arrangements mentioned above, after the spring is substantially collapsed, a small amount of residual ink remains in the ink bag which is never used. Accordingly, further spring designs have been investigated with the objective of further minimizing the amount of residual ink left stranded in the cartridge after full collapse of the ink bag.